package org.apache.lucene.util;
/**
 * Copyright 2009 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.FieldCache;
import org.apache.lucene.search.FieldCache.CacheEntry;

/** 
 * Provides methods for sanity checking that entries in the FieldCache 
 * are not wasteful or inconsistent.
 * </p>
 * <p>
 * Lucene 2.9 Introduced numerous enhancements into how the FieldCache 
 * is used by the low levels of Lucene searching (for Sorting and 
 * ValueSourceQueries) to improve both the speed for Sorting, as well 
 * as reopening of IndexReaders.  But these changes have shifted the 
 * usage of FieldCache from "top level" IndexReaders (frequently a 
 * MultiReader or DirectoryReader) down to the leaf level SegmentReaders.  
 * As a result, existing applications that directly access the FieldCache 
 * may find RAM usage increase significantly when upgrading to 2.9 or 
 * Later.  This class provides an API for these applications (or their 
 * Unit tests) to check at run time if the FieldCache contains "insane" 
 * usages of the FieldCache.
 * </p>
 * @lucene.experimental
 * @see FieldCache
 * @see FieldCacheSanityChecker.Insanity
 * @see FieldCacheSanityChecker.InsanityType
 */
public final class FieldCacheSanityChecker {

    private RamUsageEstimator ramCalc = null;

    public FieldCacheSanityChecker() {
        /* NOOP */
    }

    /**
     * If set, will be used to estimate size for all CacheEntry objects 
     * dealt with.
     */
    public void setRamUsageEstimator(RamUsageEstimator r) {
        ramCalc = r;
    }

    /** 
     * Quick and dirty convenience method
     * @see #check
     */
    public static Insanity[] checkSanity(FieldCache cache) {
        return checkSanity(cache.getCacheEntries());
    }

    /** 
     * Quick and dirty convenience method that instantiates an instance with 
     * "good defaults" and uses it to test the CacheEntrys
     * @see #check
     */
    public static Insanity[] checkSanity(CacheEntry... cacheEntries) {
        FieldCacheSanityChecker sanityChecker = new FieldCacheSanityChecker();
        // doesn't check for interned
        sanityChecker.setRamUsageEstimator(new RamUsageEstimator(false));
        return sanityChecker.check(cacheEntries);
    }

    /**
     * Tests a CacheEntry[] for indication of "insane" cache usage.
     * <p>
     * <B>NOTE:</b>FieldCache CreationPlaceholder objects are ignored.
     * (:TODO: is this a bad idea? are we masking a real problem?)
     * </p>
     */
    public Insanity[] check(CacheEntry... cacheEntries) {
        if (null == cacheEntries || 0 == cacheEntries.length)
            return new Insanity[0];

        if (null != ramCalc) {
            for (int i = 0; i < cacheEntries.length; i++) {
                cacheEntries[i].estimateSize(ramCalc);
            }
        }

        // the indirect mapping lets MapOfSet dedup identical valIds for us
        //
        // maps the (valId) identityhashCode of cache values to 
        // sets of CacheEntry instances
        final MapOfSets<Integer, CacheEntry> valIdToItems = new MapOfSets<Integer, CacheEntry>(new HashMap<Integer, Set<CacheEntry>>(17));
        // maps ReaderField keys to Sets of ValueIds
        final MapOfSets<ReaderField, Integer> readerFieldToValIds = new MapOfSets<ReaderField, Integer>(new HashMap<ReaderField, Set<Integer>>(17));
        //

        // any keys that we know result in more then one valId
        final Set<ReaderField> valMismatchKeys = new HashSet<ReaderField>();

        // iterate over all the cacheEntries to get the mappings we'll need
        for (int i = 0; i < cacheEntries.length; i++) {
            final CacheEntry item = cacheEntries[i];
            final Object val = item.getValue();

            // It's OK to have dup entries, where one is eg
            // float[] and the other is the Bits (from
            // getDocWithField())
            if (val instanceof Bits) {
                continue;
            }

            if (val instanceof FieldCache.CreationPlaceholder)
                continue;

            final ReaderField rf = new ReaderField(item.getReaderKey(), item.getFieldName());

            final Integer valId = Integer.valueOf(System.identityHashCode(val));

            // indirect mapping, so the MapOfSet will dedup identical valIds for us
            valIdToItems.put(valId, item);
            if (1 < readerFieldToValIds.put(rf, valId)) {
                valMismatchKeys.add(rf);
            }
        }

        final List<Insanity> insanity = new ArrayList<Insanity>(valMismatchKeys.size() * 3);

        insanity.addAll(checkValueMismatch(valIdToItems, readerFieldToValIds, valMismatchKeys));
        insanity.addAll(checkSubreaders(valIdToItems, readerFieldToValIds));

        return insanity.toArray(new Insanity[insanity.size()]);
    }

    /** 
     * Internal helper method used by check that iterates over 
     * valMismatchKeys and generates a Collection of Insanity 
     * instances accordingly.  The MapOfSets are used to populate 
     * the Insanity objects. 
     * @see InsanityType#VALUEMISMATCH
     */
    private Collection<Insanity> checkValueMismatch(MapOfSets<Integer, CacheEntry> valIdToItems, MapOfSets<ReaderField, Integer> readerFieldToValIds, Set<ReaderField> valMismatchKeys) {

        final List<Insanity> insanity = new ArrayList<Insanity>(valMismatchKeys.size() * 3);

        if (!valMismatchKeys.isEmpty()) {
            // we have multiple values for some ReaderFields

            final Map<ReaderField, Set<Integer>> rfMap = readerFieldToValIds.getMap();
            final Map<Integer, Set<CacheEntry>> valMap = valIdToItems.getMap();
            for (final ReaderField rf : valMismatchKeys) {
                final List<CacheEntry> badEntries = new ArrayList<CacheEntry>(valMismatchKeys.size() * 2);
                for (final Integer value : rfMap.get(rf)) {
                    for (final CacheEntry cacheEntry : valMap.get(value)) {
                        badEntries.add(cacheEntry);
                    }
                }

                CacheEntry[] badness = new CacheEntry[badEntries.size()];
                badness = badEntries.toArray(badness);

                insanity.add(new Insanity(InsanityType.VALUEMISMATCH, "Multiple distinct value objects for " + rf.toString(), badness));
            }
        }
        return insanity;
    }

    /** 
     * Internal helper method used by check that iterates over 
     * the keys of readerFieldToValIds and generates a Collection 
     * of Insanity instances whenever two (or more) ReaderField instances are 
     * found that have an ancestry relationships.  
     *
     * @see InsanityType#SUBREADER
     */
    private Collection<Insanity> checkSubreaders(MapOfSets<Integer, CacheEntry> valIdToItems, MapOfSets<ReaderField, Integer> readerFieldToValIds) {

        final List<Insanity> insanity = new ArrayList<Insanity>(23);

        Map<ReaderField, Set<ReaderField>> badChildren = new HashMap<ReaderField, Set<ReaderField>>(17);
        MapOfSets<ReaderField, ReaderField> badKids = new MapOfSets<ReaderField, ReaderField>(badChildren); // wrapper

        Map<Integer, Set<CacheEntry>> viToItemSets = valIdToItems.getMap();
        Map<ReaderField, Set<Integer>> rfToValIdSets = readerFieldToValIds.getMap();

        Set<ReaderField> seen = new HashSet<ReaderField>(17);

        Set<ReaderField> readerFields = rfToValIdSets.keySet();
        for (final ReaderField rf : readerFields) {

            if (seen.contains(rf))
                continue;

            List<Object> kids = getAllDescendantReaderKeys(rf.readerKey);
            for (Object kidKey : kids) {
                ReaderField kid = new ReaderField(kidKey, rf.fieldName);

                if (badChildren.containsKey(kid)) {
                    // we've already process this kid as RF and found other problems
                    // track those problems as our own
                    badKids.put(rf, kid);
                    badKids.putAll(rf, badChildren.get(kid));
                    badChildren.remove(kid);

                } else if (rfToValIdSets.containsKey(kid)) {
                    // we have cache entries for the kid
                    badKids.put(rf, kid);
                }
                seen.add(kid);
            }
            seen.add(rf);
        }

        // every mapping in badKids represents an Insanity
        for (final ReaderField parent : badChildren.keySet()) {
            Set<ReaderField> kids = badChildren.get(parent);

            List<CacheEntry> badEntries = new ArrayList<CacheEntry>(kids.size() * 2);

            // put parent entr(ies) in first
            {
                for (final Integer value : rfToValIdSets.get(parent)) {
                    badEntries.addAll(viToItemSets.get(value));
                }
            }

            // now the entries for the descendants
            for (final ReaderField kid : kids) {
                for (final Integer value : rfToValIdSets.get(kid)) {
                    badEntries.addAll(viToItemSets.get(value));
                }
            }

            CacheEntry[] badness = new CacheEntry[badEntries.size()];
            badness = badEntries.toArray(badness);

            insanity.add(new Insanity(InsanityType.SUBREADER, "Found caches for descendants of " + parent.toString(), badness));
        }

        return insanity;

    }

    /**
     * Checks if the seed is an IndexReader, and if so will walk
     * the hierarchy of subReaders building up a list of the objects 
     * returned by obj.getFieldCacheKey()
     */
    private List<Object> getAllDescendantReaderKeys(Object seed) {
        List<Object> all = new ArrayList<Object>(17); // will grow as we iter
        all.add(seed);
        for (int i = 0; i < all.size(); i++) {
            Object obj = all.get(i);
            if (obj instanceof IndexReader) {
                IndexReader[] subs = ((IndexReader) obj).getSequentialSubReaders();
                for (int j = 0; (null != subs) && (j < subs.length); j++) {
                    all.add(subs[j].getCoreCacheKey());
                }
            }

        }
        // need to skip the first, because it was the seed
        return all.subList(1, all.size());
    }

    /**
     * Simple pair object for using "readerKey + fieldName" a Map key
     */
    private final static class ReaderField {
        public final Object readerKey;
        public final String fieldName;

        public ReaderField(Object readerKey, String fieldName) {
            this.readerKey = readerKey;
            this.fieldName = fieldName;
        }

        @Override
        public int hashCode() {
            return System.identityHashCode(readerKey) * fieldName.hashCode();
        }

        @Override
        public boolean equals(Object that) {
            if (!(that instanceof ReaderField))
                return false;

            ReaderField other = (ReaderField) that;
            return (this.readerKey == other.readerKey && this.fieldName.equals(other.fieldName));
        }

        @Override
        public String toString() {
            return readerKey.toString() + "+" + fieldName;
        }
    }

    /**
     * Simple container for a collection of related CacheEntry objects that 
     * in conjunction with each other represent some "insane" usage of the 
     * FieldCache.
     */
    public final static class Insanity {
        private final InsanityType type;
        private final String msg;
        private final CacheEntry[] entries;

        public Insanity(InsanityType type, String msg, CacheEntry... entries) {
            if (null == type) {
                throw new IllegalArgumentException("Insanity requires non-null InsanityType");
            }
            if (null == entries || 0 == entries.length) {
                throw new IllegalArgumentException("Insanity requires non-null/non-empty CacheEntry[]");
            }
            this.type = type;
            this.msg = msg;
            this.entries = entries;

        }

        /**
         * Type of insane behavior this object represents
         */
        public InsanityType getType() {
            return type;
        }

        /**
         * Description of hte insane behavior
         */
        public String getMsg() {
            return msg;
        }

        /**
         * CacheEntry objects which suggest a problem
         */
        public CacheEntry[] getCacheEntries() {
            return entries;
        }

        /**
         * Multi-Line representation of this Insanity object, starting with 
         * the Type and Msg, followed by each CacheEntry.toString() on it's 
         * own line prefaced by a tab character
         */
        @Override
        public String toString() {
            StringBuilder buf = new StringBuilder();
            buf.append(getType()).append(": ");

            String m = getMsg();
            if (null != m)
                buf.append(m);

            buf.append('\n');

            CacheEntry[] ce = getCacheEntries();
            for (int i = 0; i < ce.length; i++) {
                buf.append('\t').append(ce[i].toString()).append('\n');
            }

            return buf.toString();
        }
    }

    /**
     * An Enumeration of the different types of "insane" behavior that 
     * may be detected in a FieldCache.
     *
     * @see InsanityType#SUBREADER
     * @see InsanityType#VALUEMISMATCH
     * @see InsanityType#EXPECTED
     */
    public final static class InsanityType {
        private final String label;

        private InsanityType(final String label) {
            this.label = label;
        }

        @Override
        public String toString() {
            return label;
        }

        /** 
         * Indicates an overlap in cache usage on a given field 
         * in sub/super readers.
         */
        public final static InsanityType SUBREADER = new InsanityType("SUBREADER");

        /** 
         * <p>
         * Indicates entries have the same reader+fieldname but 
         * different cached values.  This can happen if different datatypes, 
         * or parsers are used -- and while it's not necessarily a bug 
         * it's typically an indication of a possible problem.
         * </p>
         * <p>
         * <bPNOTE:</b> Only the reader, fieldname, and cached value are actually 
         * tested -- if two cache entries have different parsers or datatypes but 
         * the cached values are the same Object (== not just equal()) this method 
         * does not consider that a red flag.  This allows for subtle variations 
         * in the way a Parser is specified (null vs DEFAULT_LONG_PARSER, etc...)
         * </p>
         */
        public final static InsanityType VALUEMISMATCH = new InsanityType("VALUEMISMATCH");

        /** 
         * Indicates an expected bit of "insanity".  This may be useful for 
         * clients that wish to preserve/log information about insane usage 
         * but indicate that it was expected. 
         */
        public final static InsanityType EXPECTED = new InsanityType("EXPECTED");
    }

}
